Order注解用于排序
public @interface Order {
/**
* The order value.
* <p>Default is {@link Ordered#LOWEST_PRECEDENCE}.
* @see Ordered#getOrder()
*/
int value() default Ordered.LOWEST_PRECEDENCE;
}
1.OrderUtils
Spring提供了OrderUtils来获取Class的Order注解排序信息
扩展:Priority注解为javax扩展注解,功能与Order相同
public class OrderUtilsTests {
@Test
public void getSimpleOrder() {
assertEquals(Integer.valueOf(50), OrderUtils.getOrder(SimpleOrder.class, null));
}
@Test
public void getPriorityOrder() {
assertEquals(Integer.valueOf(55), OrderUtils.getOrder(SimplePriority.class, null));
}
@Order(50)
private static class SimpleOrder {}
@Priority(55)
private static class SimplePriority {}
}
2.Ordered接口
对象排序的另一种实现
public interface Ordered {
int getOrder();
}
3.OrderComparator
使用OrderComparator来比较2个对象的排序顺序
public final class OrderComparatorTests {
private final OrderComparator comparator = new OrderComparator();
@Test
public void compareOrderedInstancesBefore() {
assertEquals(-1, this.comparator.compare(
new StubOrdered(100), new StubOrdered(2000)));
}
@Test
public void compareOrderedInstancesSame() {
assertEquals(0, this.comparator.compare(
new StubOrdered(100), new StubOrdered(100)));
}
@Test
public void compareOrderedInstancesAfter() {
assertEquals(1, this.comparator.compare(
new StubOrdered(982300), new StubOrdered(100)));
}
private static final class StubOrdered implements Ordered {
private final int order;
public StubOrdered(int order) {
this.order = order;
}
@Override
public int getOrder() {
return this.order;
}
}
}
其内部比较逻辑
return (i1 < i2) ? -1 : (i1 > i2) ? 1 : 0;
- i1比i2小则返回-1
- i1比i2大则返回1
- i1等于i2则返回0
4.AnnotationAwareOrderComparator
AnnotationAwareOrderComparator继承自OrderComparator
其可以同时处理对象实现Ordered接口或@Order注解
其提供了静态方法sort,可以对List进行排序
public class AnnotationAwareOrderComparator extends OrderComparator {
}
测试代码
public class AnnotationAwareOrderComparatorTests {
@Test
public void sortInstances() {
List<Object> list = new ArrayList<>();
list.add(new B());
list.add(new A());
AnnotationAwareOrderComparator.sort(list);
assertTrue(list.get(0) instanceof A);
assertTrue(list.get(1) instanceof B);
}
@Order(1)
private static class A {
}
@Order(2)
private static class B {
}
}
5.Bean注册顺序
Demo2Config的对象将会先于Demo1Config初始化注册
注意点:其构造函数的初始化并不生效
@Configuration
@Order(2)
public class Demo1Config {
public Demo1Config()
{
System.out.println("Demo1Config");
}
@Bean
public Demo1Service demo1Service(){
System.out.println("demo1config 加载了");
return new Demo1Service();
}
}
@Configuration
@Order(1)
public class Demo2Config {
public Demo2Config()
{
System.out.println("Demo2Config");
}
@Bean
public Demo2Service demo2Service(){
System.out.println("demo2config 加载了");
return new Demo2Service();
}
}
public class Main {
public static void main(String[] args) {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext("core.annotation.order2");
}
}
输出的结果信息:
Demo1Config
Demo2Config
demo2config 加载了
demo1config 加载了
参考
http://wiselyman.iteye.com/blog/2217192
https://www.cnblogs.com/syuf/p/6846522.html
